We are requesting funds to acquire a complete virtual reality motion system that is used to study spatial orientation, motion perception, as well as the planning and execution of eye, head, hand and arm movements in human subjects. This unique system consists of a motion platform with 6 degrees of Freedom, a head-mounted visual display, an eye tracker to measure eye movements and an Optotrak system to measure head, arm and hand movements. The motion platform delivers both linear and angular motions along any direction in space. The head-mounted visual display can provide optic flow or simulated motion through more naturalistic visual environments that are either congruent or incongruent with the motion of the platform. The human motion system will be used by each of the Users to study the effects of motion environments (established by congruent visual/vestibular stimuli or cue-conflicting situations) on spatial perception, motor control and coordination. It will be used for addressing basic science questions in both normal healthy human volunteers as well as in patients with spatial orientation and/or motor deficits. The human motion system will be housed within the newly constructed Central Institute for the Deaf building at Washington University School of Medicine. Deficits in spatial orientation and motor coordination in motion environments remain poorly understood but are vital for daily functions. In humans with subjective vertigo or balance difficulties, vestibular and spatial orientation deficits are often subtle and can only be revealed by innovative and quantitative spatial orientation and motor tasks. Millions of Americans suffer from balance related deficits, particularly in older aged adults, that can lead to injury or even death from falls. The requested system will allow for state-of-the-art basic science and clinical experimentation, as well as ensure a further growth in our research endeavors and an expansion in the collaborative efforts that are already strong among the motor control and balance communities.